Worm medicines

What are worms?

Worms (sometimes called helminths) are parasites that enter the body and are able to live and feed off the person they have entered. There are many types of worms and they are usually divided into three groups:

• Roundworms - the most common roundworm infections are thought to be caused by threadworms, ascaris, hookworms and trichuris. Roundworm eggs usually enter the body by the person eating food or drinking water that contains eggs. The eggs live and hatch in the gut (intestine).

• Tapeworms - these worms live in the gut. People usually become infected by eating raw or uncooked meat.

• Flukeworms - these worms can live in the blood vessels, gut, lungs or liver. You usually become infected with flukeworms by swimming or washing in fresh water that contains flukeworms. An infection with flukeworms causes a tropical disease called schistosomiasis.

Most worm infections occur in warm tropical countries or developing countries where food and water may not be clean. It is thought that millions of people around the world are infected with worms at any one time.

In the UK the most common worm infection is threadworms - this is a type of roundworm and is sometimes referred to as a pinworm. Threadworms are spread by being in contact with someone who is already infected with threadworms. Threadworms can cause an itchy bottom.

See the separate leaflet called Itchy bottom (Pruritus ani).

Other types of worm infections can occur if you live in the UK; however, they do not occur very often. People who get these infections have usually been travelling in countries where these types of worm infections are common.

The rest of this leaflet discusses the medicines that may be used to treat worm infections.

See the separate leaflets called:

• Roundworms.

• Threadworms.

• Schistosomiasis.

Note: Despite the name, ringworm in not caused by worms. It is a name given to a type of fungal skin infection.

Which medicines are usually prescribed for worm infections?

There are several medicines that may be used to treat worm infections - they are sometimes called anthelmintics. Mebendazole is the most commonly-used threadworm medicine for kids and adults in the UK. Mebendazole is also used to treat roundworm, whipworm and hookworm infections.

Other medicines that may be prescribed for the various types of worm infections include:

• Levamisole.

• Niclosamide.

• Praziquantel.

• Albendazole.

• Diethylcarbamazine.

• Ivermectin.

• Tiabendazole.

These medicines are not licensed for use in the UK and are specially imported to treat more unusual worm infections. They are usually prescribed by doctors who specialise in treating worm infections.

How does worm medicine work?

Most medicines used to treat worm infections kill worms by either starving them or paralysing them; for example:

• Mebendazole, albendazole and tiabendazole work by preventing the worms from absorbing the sugars they need for survival. They kill the worms but not the eggs.

• Praziquantel and ivermectin work by paralysing the worms in the gut (intestine). This allows them to be easily dislodged and removed from the gut in the stools (faeces).

How long do you take worm medicine for?

In general, the length of treatment is usually quite short (at most a few days). This will depend on what type of worm you have and which medicine has been prescribed.

For example, for threadworms, mebendazole is usually given as a single one-off dose. This dose may be repeated two weeks later. For whipworm or common roundworm infections, mebendazole is given twice a day for three days.

For threadworms, it is usually advised that everybody in the household be treated if possible as this will help prevent reinfection.

Side-effects of worm medicine

It is not possible to list all the side-effects of these medicines in this leaflet. If you want more information specific to your worms medicine, see the information leaflet that came with your medicine.

In general, medicines for worms are well tolerated and very rarely cause serious side-effects.

The side-effects most commonly reported are:

• Tummy upsets such as cramps, wind, diarrhoea.

• Feeling sick (nausea).

Who cannot take worm medicine?

There are very few people who cannot take a medicine for worm infections. If for some reason one medicine has caused a side-effect or there is a reason you cannot take one, your doctor will discuss other ways to treat you.

Mebendazole is licensed for:

• Adults.

• Children over the age of 2 years.

• However, it is used to treat children from the age of 6 months if necessary.

Mebendazole is usually avoided if you are pregnant or breastfeeding. If treatment in pregnancy is considered to be absolutely necessary it is safest to give it in the second or third trimester.

Can you buy worm medicine?

For adults and for children aged over 2 years, you can buy mebendazole to treat threadworms, from your local pharmacy. If you need to treat threadworms in a child under 2 years of age, discuss this with your doctor. If you have been abroad and think you have another type of worm infection, see your doctor.